RHINOCEROS I1EMIT(ECHUS. 343 



common consent of palaeontologists lias pronounced against 

 the value of distinctive characters, derived from the lower 

 molars in the genus Ehinoceros ; but the differences above 

 indicated are so constant and well marked, that I regard 

 them as being of specific importance. 



In the < Bacon Hole' specimen (fig. 1, PI. XXI.), there are 

 two points connected with the premolars deserving notice. 

 In the penultimate (p.m. 3), the crown of which is well 

 worn, a distinct fossette is seen. This is unusual, and has 

 been caused in the present instance by the solution of a 

 portion of the valley between the horns of the posterior 

 crescent. The second point is that the last premolar is 

 double, and represented by two collateral teeth, the outer of 

 which is at a slightly lower level than the inner. The abra- 

 sion of the crowns of both these teeth, in relation to that of 

 the penultimate premolar in front, and of the first true 

 molar behind, proves that they are both of the second set, 

 and not a permanent premolar protruded excentrically along- 

 side of a retained milk molar. 



True Molars. — The antepenultimate true molar (m. 1 of 

 PL XIX.) sbows the remains of two well-marked crescents, 

 but being considerably worn it yields no distinctive cha- 

 racters. The crown is oblong, shorter than that of the 

 penultimate. Compared with the corresponding tooth of 

 B. megarhinus (Gervais, op. cit./Pl. II. fig. 8), it is narrower, 

 in reference to the length. The penultimate (m. 2) being 

 less worn shows the anterior crescent more pronounced ; the 

 posterior crescent takes a very oblique antero-posterior direc- 

 tion, its front lobe terminating near the outer third of the 

 anterior crescent ; and it represents but a small degree of cur- 

 vature. The last true molar (m. 3) is the least worn of the 

 three, the posterior crescent being distinct from and still at 

 a lower level than the anterior crescent. Its anterior division 

 presents a very pronounced horse-shoe pattern, with equal 

 limbs. The posterior division is very oblique in direction, 

 and its worn surface exhibits bat a small amount of curve. 

 TLe crown of this tooth is somewhat longer than that of the 

 penultimate. 



The dimensions of the same tooth in the same lower jaw 

 vary not a little, according to the different stages of abrasion. 

 They are all inclined a little forwards, and the length of a 

 slightly abraded crown taken at the summit is less than that 

 near the base. In consequence of difference in measurement, 

 arising from causes like these, authors are not agreed in 

 regard to the relative proportions of the different teeth, 

 more especially the penultimate and last, which are the most 

 significant. Duvernoy positively affirms that in R. tidier- 



